1. Field of the Invention
The present invention relates to engine blocks.
2. Description of the Prior Art
An engine has been heretofore well known in which vibration proof panels are mounted on a cylinder jacket side member and a crankcase side member to form a rectangular parallelopiped cylinder block so as to reduce noises without lowering the strength of the cylinder block (see Japanese Utility Model Publication No. 43486/1984).
With the recent trend of higher rotation and higher output of the engine, measures for reducing vibrations and noises thereof pose a significant task.
It is considered that the engine gives rise to vertical bending forces, longitudinal bending forces, torsion or the like, which are synergistically magnified to generate large vibrations and noises. Most of vibrations and noises of the engine are propagated to other portions through the cylinder block portion of the engine and the bearing portions of the crankshaft. It is most important to enhance the rigidity of these parts in order to reduce the vibrations and noises. However, in the aforesaid conventional engine, no measure has been taken to enhance the rigidity of the cylinder block portion. In view of the foregoing, it is contemplated that in order to enhance the rigidity of the engine, the engine block which is a vibration generating source, particularly, its cylinder block portion, is merely increased in wall thickness, reinforced by a reinforcing member such as a stiffener or formed of a high strength material. This proposal however gives rise to another inconvenience such that the weight of the engine itself is increased, the cost is considerably increased and the like.
An engine block has been known in which measures have been taken for enhancing the rigidity of the bearing portion of said cranshaft (see Japanese Patent Publication No. 202349/1983). In this proposal, no measure for lighter weight and lower cost has not been taken.
Furthermore, a vehicular engine has been known in which a lower frame is joined to the lower surface of a cylinder block by means of bolts, a crankshaft is rotatably carried between the joined surfaces thereof, and an oil pan is fixedly mounted on the lower surface of the lower frame by means of further bolts (see U.S. Pat. No. 4,753,201 specification). However, in such an engine as described above, the cylinder block and the lower frame, and the lower frame and the oil pan are respectively directly fixed together by separate bolts. A further task arises such that an increase in weight and an increase in cost result due to the increase in the number of bolts, and in addition, since the lower frame and the oil pan are directly fixed, the vibration of the engine generated during operation is transmitted from the lower frame to the oil pan, and the noise is promoted by the vibration of the oil pan itself.
Furthermore, the vibration of the engine during operation is also transmitted to the joined surfaces between the cylinder block and the transmission case through the cylinder block. Insufficient rigidity at the joined surfaces causes the vibration and noise to be increased, and therefore the coupling rigidity of the joined surfaces between the cylinder block and the transmission case is desired to be enhanced as a further measure for reducing the vibration and noise of the engine. This measure may not yet provide a satisfactory result in the conventional structure.
Moreover, in the conventional cylinder block, a solid cylinder barrel wall surrounding a cylinder bore is formed with fluid passages such as a lubricating oil passage, a cooling water passage and the like (see Japanese Patent Publication Nos. 27526/1988 and 37246/1988).
However, in the conventional engines as described above, since there naturally involves a limitation in that the cylinder barrel wall surrounding the cylinder bore is formed with the aforesaid fluid passages, most of the fluid passages are composed of a group of pipes separate from the cylinder block. Therefore, there poses a further task in that not only the number of parts increases to increase the cost but also, since the group of pipes are overhung on the cylinder block, they vibrate to promote the vibration and noise of the engine itself.